For 15 years, the United Nations has been observing "World Water Day," a time to consider the opportunities and challenges presented by a resource essential to the environment and to humankind.

It's becoming clear now that climate change may be altering the way people and governments think about water.

The UN reported this week that the world's glaciers are melting at "an alarming rate." Like reservoirs, glaciers store water and then release it at predictable rates, around which humans have formed communities and built economies. Agency France-Presse, the French news service, quotes Achim Steiner, executive director of the United Nations Environment Program, as saying:

"Millions if not billions of people depend directly or indirectly on these natural water storage facilities for drinking water, agriculture, industry, and power generation during key parts of the year."

"While I'm always cautious about 'water wars,' certainly the potential for water to become a trigger for more tension and, where there's already conflict, to exacerbate conflict is another issue that's not hypothetical."